The invention relates to a device for controlling the knitting positions of the needles of a knitting machine, of the kind in which each needle is mounted for longitudinal sliding in a guide trick and comprises at least one needle latch adapted to oscillate between two stops and provided with two butts near its respective ends, the butts being adapted to project from the trick and to be respectively and alternately retracted therein, the device comprising selection means for bringing the latches against one or more of the stops and thus selectively placing the butts in the projecting position, the device also comprising cams disposed opposite the latches and drive means for bringing about relative motion between the cams and the latches transversely to the guide tricks so that the cams exert pressure on the projecting butts in the longitudinal direction of the tricks as a result of the relative motion.
Difficult problems occur in controlling the knitting positions of the needles of a knitting machine in which each needle can occupy two or even three knitting positions plus one or two transfer positions, since it is extremely difficult to continuously monitor the position of the needle in its trick and in two opposite directions. If the needle is left to itself in either direction, there is a risk that the needle will move inadvertently, since the needle is subjected to various stresses which tend to move it along its guide trick and result in faults in the knitting. The stresses may come from the thread engaging the needle or from abrupt acceleration and impacts between the guide butts and the cams.
The conventional method of avoiding inadvertent movement of the needles consist in producing sufficient friction between the guide tricks and the needles, so that the needles are gripped between the two opposite edges of their respective tricks. Clearly this method has disadvantages even if it partly solves the problem. The friction increases the pressure between the cams and the butts on the needles and thus limits the permissible accelerations and consequently the speed of the loom. The friction on the needles increases the wear on the components and consequently the maintenance cost. It is also necessary to operate the machine at slow speed after cold starting, until it reaches a certain temperature after several hours of operation. In order to increase the speed of knitting looms, it will undoubtedly be necessary to solve the problem of controlling the needles.
An object of the invention is to provide a knitting machine in which the knitting needles are constantly guided in both directions of motion along their respective tricks, thus making it possible to considerably reduce the friction of the needles in the tricks.